The present invention is directed to integrated circuits. More particularly, the invention provides a method for making a split dual gate field effect transistor. Merely by way of example, the invention has been applied to a logic system. But it would be recognized that the invention has a much broader range of applicability.
Integrated circuits or “ICs” have evolved from a handful of interconnected devices fabricated on a single chip of silicon to millions of devices. Current ICs provide performance and complexity far beyond what was originally imagined. In order to achieve improvements in complexity and circuit density (i.e., the number of devices capable of being packed onto a given chip area), the size of the smallest device feature, also known as the device “geometry”, has become smaller with each generation of ICs. Semiconductor devices are now being fabricated with features less than a quarter of a micron across.
Increasing circuit density has not only improved the complexity and performance of ICs but has also provided lower cost parts to the consumer. An IC fabrication facility can cost hundreds of millions, or even billions, of dollars. Each fabrication facility will have a certain throughput of wafers, and each wafer will have a certain number of ICs on it. Therefore, by making the individual devices of an IC smaller, more devices may be fabricated on each wafer, thus increasing the output of the fabrication facility. Making devices smaller is very challenging, as a given process, device layout, and/or system design often work down to only a certain feature size.
An example of such a limit is how to reduce the transistor leakage current and improve the transistor drive current. For example, reducing the source-drain voltage of a transistor can lower the active power, but doing so often reduces the transistor drive current. The transistor drive current can be improved by reducing the threshold voltage and thinning the gate dielectric, but such actions often raise the transistor leakage current.
From the above, it is seen that an improved method for making a transistor structure is desired.